The present invention relates to the use of terpolymers of ethylacrylate/methacrylic acid/unsaturated carboxylic acid ester of alcohols or ethoxylated carboxylic acids as anti-settling agents in coal water slurries.
One of the major problems involved in the use of coal water slurries is the transportation by pumping of the finely divided coal particles in an aqueous system particularly when the coal content is over 50% by weight. This is because the coal particles tend to settle out when the solids content is high and cause blockages in the pumping system.
However, for efficiency in transport and burning of the coal water slurry it is desirable to increase the coal content to more than 50% by weight. Moreover, by increasing the coal content, the amount of scarce water resources needed is reduced. The reduction in the volume of water in coal water slurry increases the efficiency of the coal burning process since less heat energy is required to vaporize the water present. Therefore, it is important to be able to provide a solution to the problem of pumping coal water slurries wherein the coal content is greater than 50% by weight.
Prior attempts to improve pumping of coal water slurries include the use of anionic sulfonated surfactants (see Funk U.S. Pat. No. 4,282,006 and U.S. Pat. No. 4,330,301), and anionic sulfomethylated polyhydroxy polyphenyl compounds as dispersants (see Marcellis et al, U.S. Pat. No. 4,501,594).
Funk, U.S. Pat. No. 4,282,006 describes a method wherein coal is ground to a specified range of particle sizes such that there is a minimum of void space and a maximum surface area to enhance dispersing effects generated by electrolytes and/or dispersing agents added to the slurry.
Yamamura et al, U.S. Pat. No. 4,330,301 describes sulfonated polycyclic aromatic compounds, salts thereof and formaldehyde condensates thereof as dispersants.
It is also known to use xanthan gum to prevent the coal particles from settling. However, the natural gums have a tendency to be degraded by bacteria and heat. Moreover, xanthan gum excessively increases the viscosity of the coal water slurry and causes difficulties in pumping.
Terpolymers of ethylacrylate, methacrylic acid and itaconic acid has been reported for use as thickeners for latex based paints. See published U.K. Patent Application No. 2,127,836A and EPO Patent Application No. 0109820. These have not been described as being suitable for coal water slurries as anti-settling agents. Moreover, because of the high solids content desired in coal water slurries for efficient pumping, it is undesirable to significantly increase the viscosity of coal water slurries.
Therefore, it is an objective to provide a method of preventing the coal particles from settling out of solution without significantly increasing the viscosity of the system.
It is further objective to provide anti-settling agents useful in coal water slurries that is simple to use and easy to obtain.